Ensemble RXTX - Home Page Band: 30, 20, 17m

This is the successor website (wb5rvz.org) for the Ensemble RXTX, originally documented on the
wb5rvz.com site

Introduction

General Info

Announcement - Official Site

This site is now the officially maintained site for the Ensemble RXTX kit. The previous documentation on www.wb5rvz.com is no longer being maintained. If you are curious, you can still pop over to the previous site to see the original documentation, but be advised that it is no longer being maintained there.

These notes were developed as the author built the pre-production version of the kit (4/4/2010), resulting in some minor rearrangements of layouts. These will cause the "completed" pictures at the end of each stage to be slightly different, due to the layout changes between that version and the currently documented production version.

This kit is an SDR Transceiver that follows in the very successful line of RXTX Softrocks, the most recent being the RXTX V6.3 multi-band transceiver. The Ensemble kit is essentially the RXTX V6.3, but with its band-specific components fixed and predetermined (as opposed to the plug-in daughtrer boards for these functions in the RXTX V6.3). The kit, therefore, is not compatible with the Mobo series of add-ons, since they depend upon the plug and socket arrangements of the RXTX V6.3. The kit comes in five versions, corresponding to five "super-bands":

Once you have decided on your band choice, you can select the band by clicking on the "Bands" tab at the top of any page on the Ensemble RXTX website. This will customize these notes (and theid component values) for the selected band option. The band selection will hold for the duration of your "session" on the website and while in the Ensemble RXTX portion. Get in the habit of checking the header on each page to be sure your band selection is still in effect.

In each version, the radio has complete frequency agility within the "super-band" (thanks to the reliable Si570 programmable oscillator), limited only by the fixed/installed band-specific components. This means that, for example, with the 30/20/17m version, the user can operate all modes on all three of those ham bands, anywhere in those bands, subject only to the limitations of their license and the SDR software being used. In fact, the kit can also receive any HF signals within the installed "super-band".

The kit provides an Atmel AVRMicrocontroller on-board, programmed to act as a USB device and installed in a galvanically isolated section of the board. Achange from the earlier transceivers is the addition of jumpers on board to switch the ring and tip assignments of RX and TX I and Q signals.

Another welcome change from the earlier models is that all connections to the outside world are handled via on-board jacks (provided with the kit).

The kit is offered with all of the parts necessary to build it for any one of the five possible versions. Consequently, the builder will always have some parts "left-over" at the end of the build. These documents contain band-specific Bill of Materials listings for each version (in addition to the Bill of Materials for the parts of the radio that are not band-specific.

One Builder's Experience - Bill Fahle K5WL

For an excellent description of how it is to build this kit, check out Bill's posting here at this link. Per Bill: "Here are some notes from my build (I'm a novice, and I did manage to get through it eventually, but the things I learned about troubleshooting might be helpful to others)." This is great stuff - way to go, Bill!

Availability

Tony Parks has released the following information concerning availability and pricing of this kit (message dated 5/21/2010):

Recent test results with RXTX Ensemble prototype units gives me confidence that the kit is ready for production. Later today 200 circuit boards will be placed on order so that 200 kits can be made available starting the second week of June.

The RXTX Ensemble kit will include all components so that the kit may be built as a one watt SDR transceiver for one of four band groups: 160m, or 80m/40m, 40m/30m/20m, or 30m/20m/17m, or 15m/12m/10m.

The kit price is $89 plus $3 for US postage or $6 for DX postage. DX kit mailing will be made in two padded envelopes to keep the value of each envelope low. (The $89 kit price compares well to the total price of $84 for the equivalent functions in the v6.3 RXTX.)

You should read through these instructions thoroughly before commencing the build.
As a convenience, should you like to use it, there is a page that provides a very
abbreviated list of build notes for each stage,
along with the relevant topside
and bottomside board layouts. You could run that page and print it out for use during
the actual build of the stage.

Theory of Operation

Refer to the block diagram below

(click on any block in the diagram to go to the build stage which implements that block)

Foundation Circuitry

The transceiver is controlled by an Attiny85 microcontroller, programmed as a USB device to provide PTT control, paddles input, and local oscillator frequency control, in a galvanically isolated area of the PCB.

Power (+5 Vdc) for this section is provided by the USB bus from the PC. Power for the programmable local oscillator is provided by converting the USB bus power down to 3.3 Vdc (in the USB Power stage).

The function of the local oscillator is to produce a signal whose frequency is four times the desired "center frequency" of the radio. The "center frequency", plus the sound card in the PC, will determine the width of the "chunk of spectrum" one will see in the RX (and TX) display on the PC's screen - i.e., the available, visible bandwidth. This bandwidth is represented as a number of kHz either side of the "center frequency. That number of kHz is half of the sound card's sampling rate. Normal sampling rates are 48 kHz, 96 kHz, and 192 kHz (corresponding to bandwidths of the "center frequency" plus or minus 24 kHz, 48 kHz, and 96 kHz, respectively. The sampling rate of the sound card is directly proportional to the cost of the sound card - the higher the rate, the higher the cost.

The output of the local oscillator is fed to the dividers stage, where the signal is divided by 4, yielding two signals which are identical except that they are 90 degrees out of phase with each other - i.e., in quadrature. These signals are at the "center frequency" and will clock both the RX mixer and the TX mixer.

RX Circuitry

The transceiver has a common antenna terminal and RF path which is switched between the RX Bandpass filters (default) and the TX low-pass filters, via circuitry in the RF I/O and Switching Stage. The switching is performed in response to the /PTT signal from the microcontroller, as selected by the SDR program on the PC. In the RX chain, the incoming RF is band-pass filtered in T5/L4/C39, with the RF output at T5's secondaries in antiphase.

The antiphase RF signals out of T5 are coupled into the RX Mixer Stage via R53 and R54. The mixer chip (actually a commutating switch, clocked by the two QSD Clock signals from the Dividers Stage) outputs the product and difference signals of the incoming RF against the QSD clock. The effect is to down-convert the incoming RF into its quadrature analogues at frequencies ranging from 0 to roughly 100 kHz.

These quadrature pairs from the RX Mixer, identifcal in all respects except phase, are fed to the RX OpAmp Stage for amplification and filtering into the audio and infra-audio range and delivered to the RX output stereo audio jack, J4, to be input to the PC's STEREO input (line-in or Mic).

The PC's sound card performs a conversion of the two analog signals ("I and Q") to a digital representation, which is then operated upon by modules of the SDR program to perform the many "radio" functions, such as demodulation, filtering, AGC, etc., that are expected of a fine receiver. To do this, it absolutely essential that the soundcard being used supports STEREO input. The sampling rate, quality and specs of the soundcard will determine whether and how well the PC can work signals whose frequency is either sode of the center frequency. Common sound card sampling ratesfor this bandwidth are 48 kHZ, 96 kHz, and 192 kHz. These each correspond to the ability to support SDR processing of "chunks" of bandwidth of 48 kHz, 96 kHz, and 192 kHz, each chunk centered on the center frequency (CF), with "wings" on either side of the CF that are one-half the sampling rate in width.

TX Circuitry

The transmit functionality is essentially the reverse of the RX functionality. In the PC, rather than demodulating input I and Q signals as in the RX, the PC modulates the digital signals (from the microphone or a keyer module. for example) into analog I and Q (infra) audio STEREO outputs, typically output to the line-out jack on the soundcard. The I and Q signals at the line-out are in quadrature (identical in all respects save phase) and appear at stereo jack J3. There are fed to the TX OpAmp Stage. This unitary gain stage translates the I and Q signals into four equal signals, at 0, 90, 180, and 270 degrees of phase.

These four signals from the TX Opamp Stage are coupled via R25-R28 to the TX Mixer Stage. Just as the RX Mixers "mixed" incoming RF with the QSD clock (center frequency) signals to produce (infra)audio signals, the TX Mixer does the reverse, "mixing" modulated (infra) audio signals with the QSE RF clock signals to produce up-converted RF outputs that are analogues of the TX I and Q inputs. This modulated RF output of the TX Mixer (aka "Quadrature Sampling Exciter", or "QSE") is coupled via T2, C20, L1, and C21 to the Driver/PA stage.

The Driver/PA stage shapes and amplifies the modulated RF output from the TX Mixer stage and feeds the result to the antenna path as switched by the PTT switching circuitry. The switching circuitry activates the Driver/PA stage and forces a S12 line to high (approximately 12 Vdc), to permit switching an external amplifier. This stage will deliver approximately one watt of output into a 50 ohm load.

Project Bill of Materials

The Ensemble RXTX kit has an extensive Bill of Materials. The kit contains
sufficient parts to build any one of the several band-coverage options. To aid the builder
throughout the build, the bill of materials will be presented in several different ways:

Traditional Project Level Bill of Materials - for selected band
(click to view)

Ensemble RXTX Detailed Build Notes

For the non-expert builders among us, this site takes you through a stage-by-stage
build of the kit. Each stage is self-contained and outlines the steps to build and
test the stage. This ensures that you will have a much better chance of success
once you reach the last step, since you will have successfully built and tested
each preceding stage before moving on to the next stage.

Each stage is listed below, in build order, and you can link to it by clicking on
its name below (or in the header and/or footer of each web page).

Stage-By-Stage Testing

Each stage will have a "Testing" Section, outlining one or more tests that, when
successfully completed, provide you with the confidence and assurance that you are
heading in the right direction towards a fully tested and built transceiver.

When you perform a test, you should always record the results of the test where
indicated in the Testing section. This will make troubleshooting via the reflector
much easier, since you will be communicating with the experts using a standard testing
and measurement regime.

When comparing measurements to those published in these notes, the builder should
be aware that actual and expected values could vary by as much as +/- 10%. The idea
behind furnishing "expected/nominal" measurement values is to provide the builder
with a good, "ballpark" number to determine whether or not the test has been successful.
If the builder has concerns about his measurements, he should by all means pose
those concerns as a query in the Softrock reflector so the experts can provide assistance.

It goes without saying that you should ALWAYS precede any tests with a very careful,
minute inspection (using the best light and magnification available to you) to be
sure all solder joints are clean and there are no solder bridges or cold joints.

This kit can be built and reliably tested using nothing more than a common multimeter.
Tests assume that the builder has a decent digital multimeter of sufficiently high
input impedance as to minimize circuit loading issues. Measurements will be
taken of current draws, test point voltages, and resistances.

Most stages will have a current draw test, in which the builder tests the stage's
current draw in two different ways:

First, testing the draw through a current-limiting resistor

Then, when that test is OK, removing the current-limiting resistor and measuring
the real current draw.

Some tests will require you to use your ham radio to receive or generate a signal
of a specified frequency in order to test transmitters, oscillators, dividers, and/or
receivers.

Optional testing. If the builder has (access to) a dual channel oscilloscope, along
with an audio signal generator and an RF signal generator, and feels the need to
perform tests beyond the basic DMM tests, certain stages will include in their testing
section some optional tests involving this advanced equipment.

The IQGen or
DQ-Gen programs
available free from Michael Keller, DL6IAK, can be used in a pinch to get the sound
card to produce audio tones for injection into the circuit.

You can always use Rocky to generate I and Q signals for tests requiring these audio
signals (this is the author's preferred way)

XFRMR: 1.74uH 11T bifilar/22T #30 on T30-6(yellow) Primary: Using approximately 14 inches of #30 wire, wind 11 turns , bifilar, on a 0.30 inch od T30-6 (yellow) ferrite.Secondary: Using 14 inches of #30 wire, wind 22 turns on the ferrite in the same direction as the primary winding. Inductance of the single winding (usually the primary) is 1.74 uH.

T3

XFRMR: 6T/3T bifilar #30 on BN-61-2402 Primary: Using approximately 6 inches of #30 wire, wind 6 turns on a BN-61-2402 ferrite.Secondary: Using a total of 6 inches of #30 wire, wind 3 turns , bifilar, on the ferrite in the same direction as the primary winding. Inductance of the single winding (usually the primary) is 9.00 uH.

T4

XFRMR: 3T bifilar/5T #30 0n BN-61-2402 Primary: Using approximately 6 inches of #30 wire, wind 3 turns , bifilar, on a BN-61-2402 ferrite.Secondary: Using 5 inches of #30 wire, wind 5 turns on the ferrite in the same direction as the primary winding. Inductance of the single winding (usually the primary) is 6.25 uH.

T5

XFRMR: 0.6uH: 14T/2x7T bifilar #30 on T25-6 (yellow) 8"Primary: Using approximately 8 inches of #30 wire, wind 14 turns on a 0.25 inch od T25-6 (yellow) ferrite.Secondary: Using a total of 8 inches of #30 wire, wind 7 turns , bifilar, on the ferrite in the same direction as the primary winding. Inductance of the single winding (usually the primary) is 0.60 uH.

T6

XFRMR: 4T bifilar #30 on BN-61-2402 Primary/Secondary using a total of approximately 7 inches of #30 wire, wind 4 turns , bifilar, on a BN-61-2402 ferrite.Inductance of the single winding (usually the primary) is 4.00 uH.

Component Identification

After soldering problems, the most common cause of trouble in kit building is the
installation of the incorrect component. Most often this is the case with resistors
(hint - if voltage or current draw tests are way out of whack, suspect resistors or solder bridges).
Invest in a cheap multimeter and MEASURE the resistance. As Pete, M0FMT, said:
" ... then you don't have to worry about this modern trend of poor identification of components.
I doubt you will find an issue with Tony's kits but measuring is best. A cheap OVA meter
costs 2 or 3 bucks and a simple cap bridge is easy to build. (you can search E-Bay for
"L/C/F Inductance Capacitance High Precision Meter" and will find several digital L/C
meters for $20-$30) These two bits of kit are
worth there wieght in gold. Oh and most meters have diode and transistor testers build
in... remarkable when you think back to the darkages when I were a lad."

It cannot be overstressed: do not rely solely on the color codes for
identification of the correct resistor; ALWAYS measure with your ohmmeter as
a double check. Measure twice, cut once.

You may also want to review the information from the HamNation series
on George, W5JDX, and his build of the Softrock Ensemble RXTX. He uses
an inexpensive heat gun and Solder paste to install SMT capacitors and ICs.
The Session where he introduces the process is in
Episode #70 at 36 minutes, 30 seconds
into the podcast.

For the more adventurous, there is a process using solder paste and an electric
oven called the reflow process, which can be used to install all the SMT chips to
one side of the PC Board. This is documented by Guenael Jouchet in the following
Youtube segment:

Solder Stations. Don't skimp here. Soldering deficiencies
account for 80 percent of the problems surfaced in troubleshooting. It is preferable
to have an ESD-safe station, with a grounded tip. A couple of good stations that
are relatively inexpensive are:

Work Area

You will need a well-lit work area and a minimum of 3X magnification (the author
uses a cheap magnifying fluorescent light with a 3X lens. This is supplemented by
a hand-held 10 X loupe - with light - for close-in inspection of solder joints and
SMT installation.

You should use a cookie sheet or baking pan (with four sides raised approximately
a half an inch) for your actual work space. It is highly recommended for building
on top of in order to catch stray parts, especially the tiny SMT chips which, once
they are launched by an errant tweezer squeeze, are nigh on impossible to find if
they are not caught on the cookie sheet.

Misc Tools

It is most important to solidly clamp the PCB in a holder when soldering. A "third-hand"
(e.g.,
Panavise or the Hendricks kits PCB
Vise) can hold your board while soldering. In a pinch, you
can get by with a simple
third-hand, alligator clip vise. Jan G0BBL suggests "A very cheap way is
to screw a Large Document Clip to a woodblock which will clamp the side of a PCB."